feat: add solutions to lc problems: No.3992, No.3993, No.3996, No.3997

[yanglbme]

Summary

• Add multi-language solutions (Python/Java/C++/Go/TypeScript) for problems 3992, 3993, 3996, and 3997
• Complete bilingual README solution explanations for each problem

Test plan

• Spot-check solution code against README tabs for consistency
• Verify formatting (black / clang-format / prettier / gofmt)
• Sanity-check sample cases for each problem

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Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 79.8%, saving 711.7 KB.

Filename	Before	After	Improvement	Visual comparison
solution/3900-3999/3997.Count Dominant Nodes in a Binary Tree/images/t9.png	818.8 KB	167.7 KB	79.5%	View diff
solution/3900-3999/3997.Count Dominant Nodes in a Binary Tree/images/tnew.png	57.9 KB	7.9 KB	86.4%	View diff
solution/3900-3999/3996.Even Number of Knight Moves/images/knight.png	14.8 KB	4.3 KB	71.1%	View diff